Drill string and drill collar therefor

ABSTRACT

A drill string and drill collar therefor used in rotary drilling of a borehole through earth formations to substantial depths wherein the drill string includes an elongated tubular drill stem having a longitudinal axis and opposite ends thereof adapted for connection between a drill bit and a column of drill pipe to provide a drill stem for the drill bit. The drill stem has an upper end portion having a pad or pads secured thereon and extending around a minor portion of the peripheral surface thereof and the pad or pads each have a face for wiping contact with a wall of the borehole to provide lateral support for the upper end portion of the drill stem which also has a lower end portion which may have a pad secured thereon and extending around a minor portion of the peripheral surface thereof and the pad on the lower end portion when used is in longitudinal alignment with the pad on the upper end portion. The drill stem has an intermediate portion having a smaller cross section than the cross section of the upper end portion and the lower end portion. A plurality of longitudinally spaced and aligned pads are secured to the intermediate portion and each pad on the intermediate portion extends around a minor portion of the peripheral surface thereof and the plurality of pads are positioned in diametrically opposed relation with the pads or pad on the upper end portion and the pad on the lower end portion of the drill stem.

United States Patent Williams, Jr.

[ Dec. 24, 1974 DRILL STRING AND DRILL COLLAR THEREFOR [76] Inventor: Edward B. Williams, Jr., PO. Box 648 103 Mullaney Rd., Greenville, Tex. 75401 7 [22] Filed Nov. 9, 1973 [21] Appl. No.: 414,239

[52] US. Cl. 175/325, 175/76 [51] Int. Cl. E21c 9/00, E2lb 7/10 [58] Field of Search 175/61, 73, 75, 76, 325, 175/343, 376

[56] References Cited UNITED STATES PATENTS 2,173,309 9/1939 Monroe 175/76 2,745,635 5/1956 Zublin 175/76 2,841,366 7/1958 Dunn 175/325 UX 3,081,829 3/1963 Williams.... 175/376 3,160,218 12/1964 Crake l75/75 X 3,285,349 11/1966 Brandon 175/343 X 3,306,378 2/1967 Williams.... 175/325 3,382,938 5/1968 Williams 175/61 X Primary Examiner-David H. Brown Attorney, Agent, or Firm-Fishburn, Gold & Litman drilling of a borehole through earth formations to substantial depths wherein the drill string includes an elongated tubular drill stem having a longitudinal axis and opposite ends thereof adapted for connection between a drill bit and a column of drill pipe to provide a drill stern for the drill bit. The drill stem has an upper end portion having a pad or pads secured thereon and extending around a minor portion of the peripheral surface thereof and the pad or pads each have a face for wiping contact with a wall of the borehole to provide lateral support for the upper end portion of the drill stem which also has a lower end portion which may have a pad secured thereon and extending around a minor portion of the peripheral surface thereof and the pad on the lower end portion when used is in longitudinal alignment with the pad on the upper end portion. The drill stem has an intermediate portion having a smaller cross section than the cross section of the upper end portion and the lower end portion. A plurality of longitudinally spaced and aligned pads are secured to the intermediate portion and each pad on the intermediate portion extends around a minor portion of the peripheral surface thereof and the plurality of pads are positioned in diametrically opposed relation with the pads or pad on the upper end portion and the pad on the lower end portion of the drill stem.

12 Claims, 6 Drawing Figures DRILL STRING AND DRILL COLLAR THEREFOR The present invention relates to a drill string and a drill collar therefor used in rotary drilling of a borehole in earth formations to substantial depths and particularly to an improved drill collar adapted for controlling deviation of the drill bit from its intended course.

l-Ieretofore, drill collars have consisted of one or more stands of heavywalled drill pipe that are inserted into the drilling string just above the drill bit in an attempt to maintain a stiff stem for the bit. The drill collars, together with the drill pipe secured thereto, pro vide an elongated heavy weight column of metal that pushes the drill bit against the bottom of the borehole as the drill bit is rotated. Due to the length and yieldability of a string of drill pipe, the pipe bends under compression of its own weight and makes contact with the wall of the borehole at various points along the length thereof. It is evident that as the weight increases toward the bottom of the borehole, the spacing between points of contact become less and in spite of increased rigidity afforded by the drill bit toward the wall of the borehole. When the drilling operations are carried out with the drill collar in contact with the wall of the borehole, as by bending of the column of drill pipe, the axis of rotation remains in the center of the collar as it rotates about its bent axis thereby aiming the drill bit at an angle to the intended axis of the borehole. Consequently, the bit continuously deflects from its intended drilling position, to produce a crooked borehole. When the drill bit encounters a dipping formation. this deflection of the borehole is aggravated because the bit tries to drill in a direction normal to the plane of the formation.

An attempt to provide a drill string and a drill collar therefor which would overcome the aforementioned difficulties is illustrated in the US. Pat. No. 3,382,938 issued May 14, 1968, to Edward B. Williams, Jr., which discloses a drill collar of rigid character having a permanent curvature or warp toward one side having a series of pads extending therefrom to assure that if further curvature of the drill collar should occur under weight of a column of drill pipe, the curvature develops toward the side having the pads thereon to retain same in wiping contact with the wall of the borehole. It has been found that when such bending does occur, the axis of the drill bit is moved out of alignment with the axis of its intended course and even a slight deviation is cumulative particularly when drilling to substantial depths.

The drill collar of the present invention provides controlled bending of a drill stem to maintain the axis of the drill bit in alignment with the axis of its intended course while providing wiping contact of pads on the stem with the wall of the borehole. An other feature of the present invention includes means to position and maintain a gauge cutting cone of the drill bit in longitudinal alignment with a selected portion of the drill stem, and more particularly in alignment with pads on an upper end portion of the drill stem and in diametrically opposed relation with pads on an intermediate portion of the drill stem whereby the controlled bending of the drill stem maintains the gauge cutting cone in engagement with the wall and bottom-of the borehole and maintains the axis of the bit in alignment with its intended course and thereby centered in the borehole.

The principal objects of the present invention are: to provide an improved drill collar for use in a drill string adapted to overcome the aforementioned difficulties; to provide such a drill collar adapted to bend at selected points and in selected directions such that wear pads thereon contact the wall of the borehole and the wear pads are maintained at the point of contact with the wall of the borehole such that the drill collar is supported throughout substantially a major portion of its length; to provide such a drill collar wherein the wall contacting pads are adapted to guide the stem and maintain the drill bit substantially centered in the borehole; to provide such a drill collar which may be easily inserted into and removed from the borehole yet being adapted to provide sufficient guiding of the stem during drilling to maintain the drill bit on its intended course and to permit flow of drilling fluid and cuttings carried thereby around and through pads in engagement with the wall of the borehole; to provide such a drill collar having means for aligning a gauge cutting cone of a drill bit with a specific pad or aligned pads on the drill collar for optimum cutting and maintaining the drill bit entered on its intended course; to provide such a drill collar carrying a series of spaced apart pads each having faces in wiping contact with the wall of the borehole in a manner to maintain the drill bit on the desired drilling axis and prevent deviation because of a tendency of the drill bit to follow a dipping earth formation; to provide such a drill collar having pads arranged such that bending of the drill collar adjacent an intermediate portion is such that the bending develops toward the side of the intermediate portion having the pads thereon thereby retaining the pads in wiping contact with the wall of the borehole; and to provide such a drill collar which more efficiently accomplishes its intended purpose, which is easily produced without weakening the strength of the collar, which is economical to manufacture, durable in use, and particularly well adapted for the proposed uses.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of the specification and include an exemplary embodiment of the present invention and illustrate various objects and features of the drill string and the drill collar therefor.

FIG. 1 is a longitudinal sectional view of a borehole being drilled by a drilling string equipped with drill collars constructed in accordance with the present invention.

FIG. 2 is an enlarged longitudinal sectional view of the borehole showing the drilling string being lowered through the borehole with the drill collar being shown in elevation.

FIG. 3 is an enlarged longitudinal sectional view of the borehole and the drilling string and showing the drilling string after the drill bit has reached the bottom of the borehole and after drilling has started.

FIG. 4 is an enlarged transverse sectional view through an upper end portion of the drill collar and taken on line 4-4, FIG. 3.

FIG. 5 is an enlarged transverse sectional view through the intermediate portion of the drill collar and taken on line 55, FIG. 3.

FIG. 6 is an enlarged transverse sectional view through a lower end portion of the drill collar and taken on line 66, FIG. 3.

Referring more in detail to the drawings As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

In the disclosed embodiment of the present invention, the reference numeral 1 generally designates a drill collar used in rotary drilling of a borehole 2 through earth formations 3 to substantial depths. The drill collar 1 comprises an elongated tubular drill stem 4 having a longitudinal axis and opposite ends 5 and 6 thereof adapted for connection into a drilling string 7 between a drill bit 8 and a column of drill pipe 9 and to thereby provide a drill stern for the drill bit 8. The drill stem 4 has an upper end portion 10 having at least one pad 11 secured thereon and extending around a minor portion of a peripheral surface 12 of the upper end portion 10 and the pad or pads each have a face 14 positioned for wiping contact with a wall 15 of the borehole 2 thereby providing lateral support for the upper end portion 10 of the drill stem 4 which also has a lower end portion 16 which may have a pad 17 secured thereon and extending around a minor portion of a peripheral surface 18 of the lower end portion 16 and the pad 17 when used is in longitudinal alignment with the pad or pads 11 on the upper end portion 10. The drill stem 4 has an intermediate portion 20 having a smaller cross section than the upper end portion 10 and the lower end portion 16 of the drill stem 4 and having the center of gravity thereof positioned laterally of the longitudinal axis of the drill stem 4. The intermediate portion 20 has at least one and preferably a plurality of longitudinally spaced and aligned pads 21 secured to the intermediate portion 20 and each pad 21 thereon extends around a minor portion of a peripheral surface 22 of the intermediate portion 20 and the plurality of pads 21 are positioned in diametrically opposed relation with the pad or pads 11 on the upper end portion 10 and the pad 17 on the lower end portion 16.

The intermediate portion 20 of the drill stem 4 is bodily moved toward the wall 15 of the borehole 2 to move the pads 21 into wiping contact with the wall 15 of the borehole 2 in response to axial load on the drill bit 8 and rotation of the column of drill pipe 9. Controlled bending of the drill stem 4 is operative to maintain the axis of the drill bit 8 aligned with the axis of its intended course and centered in the borehole 2.

The drill bit 8 has a plurality of spaced cutting cones and one of the cutting cones is adapted to cuttingly engage the wall 15 and a bottom 23 of the borehole 2 to thereby define the gauge of the borehole 2. The other cutting cones are adapted to engage the bottom 23 only of the borehole 2. Means are provided, as later described, to maintain the gauge cutting cone in a specific position relative to the pads 21 on the intermediate portion 20 and the pad or pads 11 on the upper end portion 10 for maximum cutting by the bit 8.

The illustrated drill bit 8 is particularly adapted for drilling earth, rock and like earth formations 3 during oil industry operations. The drill bit 8 includes a body member 24 preferably having a passage extending longitudinally thereof and between an open or fluid receiving end 25 and a closed end 26 of the body member 24 and having a suitable exit into the borehole 2. The drill bit 8 has a plurality of circumferentially spaced arms or lugs 27, 28 and 29 each extending generally longitudinally and outwardly from the body member 24 adjacent the closed end 26. The lugs 27, 28 and 29 provide axle portions for rotatably mounting thereon cutting cones 30, 31 and 32 respectively. The cutting cones 30, 31 and 32 each rotate about a respective axis which intersects a longitudinal axis of the body member 24 thereby defining a respective acute angle between the respective axis and the longitudinal axis of the body member 24.

The body member 24 of the drill bit 8 is illustrated as being of a generally cylindrical shape and having a tapered pin portion 33 which has an exterior surface with threads terminating at a shoulder 34 whereby the drill bit 8 may be mounted in a box 35, as later described, in a manner to orient the cutting cones of the drill bit in a desired relation to the pad or pads 11 on the upper end portion 10 of the drill stem 4, as later described.

The drill bit 8 may have any number of cutting cones thereon, however, it has been found that three cutting cones can be arranged in a manner to provide teeth extending substantially the full transverse dimension of the drill bit 8. The cutting cones 30, 31 and 32 are circumferentially spaced and positioned on l20 centers.

One of the cutting cones, for example, the cutting cone 30, is adapted to engage the bottom 23 and the wall 15 of the borehole 12 thereby defining the gauge of the borehole 2. The other cutting cones 31 and 32 are thereby spaced from the wall 15 while engaging only the bottom 23 of the borehole 2.

The illustrated upper end portion 10 of the drill stem 4 has an internally threaded tapering box 36 adapted to receive a pin 37 of the lowermost drill pipe 9. The upper end portion 10 of the drill stem 4 has substantially the same diameter as the lowermost drill pipe 9 and has at least one pad 11 secured thereto and extending around a minor portion of the peripheral surface 12 thereof. In the illustrated structure, the pad or pads 11 each extend around of the peripheral surface 12 and terminate in side edges 38 and 39 which are substantially radial with the center or longitudinal axis of the upper end portion 10. The upper and lower ends 40 and 41 respectively of the pad or pads 1 1 are preferably inclined upwardly and downwardly respectively from the face 14. The face 14 of the pad or pads 11 is in wiping contact with the wall 15 and, therefore, the face 14 is arcuate and has a radius substantially equal to the radius of the borehole 2. In the illustrated structure, the upper end portion 10 has a length suffi cient to support two spaced pads 11 positioned in longitudinal alignment to thereby provide lateral support for the upper end portion 10 of the drill stem 4.

The drill stem 4 includes an upper tapered portion 42 extending between the upper end portion 10 and the intermediate portion 20 of the drill stem 4. When the drill stem 4 is suspended with the drill bit 8 spaced from the bottom 23 of the borehole 2, the upper tapered portion 42 is generally conical and longitudinally aligned with the upper end portion and with the intermediate portion 20. The upper tapered portion 42 is adapted to bend during bodily movement of the intermediate portion 20 toward the wall of the borehole 2.

The intermediate portion of the drill stem 4 has a cross section smaller than the cross section of the upper end portion 10 and the lower end portion 16. A major portion of the peripheral surface 22 of the intermediate portion 20 of the drill stem 4 is arcuate or generally cylindrical. A minor portion 43 of the peripheral surface 22 of the intermediate portion 20 of the drill stem 4is flat thereby providing a further decrease in the cross section of the intermediate portion 20 and in a manner to encourage bodily movement thereof toward the wall 15 of the borehole 2.

The pads 21 are mounted on the major or arcuate portion of the peripheral surface 22 of the intermediate portion 20 thereby positioning the center of gravity of the intermediate portion 20 laterally of the center of the drill stem 4. The pads 21 are longitudinally spaced and aligned and are positioned in diametrically opposed relation with the flat surface 43. The pads 21 are also positioned in diametrically opposed relation with the pad or pads 11 on the upper end portion 10 whereby during rotation of the drill stem 4, centrifugal force effects bending of the upper tapered portion 42 to move the pads 21 into wiping contact with the wall 15 of the borehole 2 at a position diametrically opposed to the position of the wiping contact of the pad or pads 11. The pads 21 each have a face spaced from the wall 15 of the borehole 2 when the drill bit 8 is spaced from the bottom 23 of the borehole 2. and in wiping contact with the wall 15 of the borehole 2 when weight of the drilling string 7 is on the drill bit 8 and the drilling string 7 is being rotated to provide lateral support for the intermediate portion 20.

The drill stem 4 includes a second or lower tapered portion 44 extending between the intermediate portion 20 and the lower end portion 16 of the drill stem 4. The lower tapered portion 44 of the drill stem 4 is similar to the upper tapered portion 42 and is also generally conical in shape when the drill stem 4 is suspended having the drill bit 8 spaced from the bottom 23 of the borehole 2. Rotation of the drilling string 7 effects bending of the lower tapered portion 44 positioning the lower end portion 16 and the drill bit 8 mounted thereon in the longitudinal center of the borehole 2.

The lower end portion 16 is substantially the same size as to the upper end portion 10 and the pad 17, when used, extends around a minor portion of the peripheral surface 18 of the lower end portion 16 and is positioned in longitudinal alignment with the pad or pads 11 on the upper end portion 10. The pad 17 has a face 45 adapted to be spaced from the wall 15 of the borehole 2 both when the drill bit 8 is spaced from the bottom 23 of the borehole 2 and also when the weight of the drilling string 7 is on the drill bit 8 with the cutting cones in engagement with the bottom 23 of the borehole 2.

It has been found that the drilling string 7 follows a substantially true course through the earth formations 3 when the gauge cutting cone has the portion thereof engaging the intersection of the wall 15 and the bottom 23 of the borehole 2 longitudinally aligned with the pads or pad 11 on the upper end portion 10 of the drill stem 4 and thereby in diametrically opposed relation with the pads 21 on the intermediate portion 20 of the drill stem 4. Therefore, the lower end portion 16 has a box 46 with an internally threaded tapered bore adapted to receive an externally threaded tapered pin 47 of a box extension 48 which is adapted to receive the tapered pin portion 33 of the drill bit 8 in the other end thereof. The pin 47 of the box extension 48 terminates at a shoulder 49 adapted to engage the end of the lower end portion 16 in a manner to align a selected point on the peripheral surface of the box extension 48 with the pad or pads 11 on the upper end portion 16. The portion of the box extension 48 receiving the tapered pin 33 of the drill bit 8 is also threaded in a manner such that when the shoulder 34 of the body member 24 of the drill bit 8 engages the end of the box extension 48, the gauge cutting cone will be aligned with the pad or pads 11 on the upper end portion 10.

It may be desirable to include a second drill stem 50 in the drilling string 7 particularly as the overall length of the drilling string 7 is increased. The second drill stem 50 has opposite ends 51 and 52 thereof adapted for connection into the column of drill pipe 9 and to the upper end portion 10 of the first drill stem 4 respectively. The second drill stem 50 has opposite end portions 53 and 54 and an intermediate portion 55 therebetween. The second drill stem 50 is substantially symmetrical about the center thereof and the end portions 53 and 54 each have two longitudinally spaced and aligned pads 56 and 57 respectively and the pads 56 on the end portion 53 are in longitudinal alignment with the pads 57 on the end portion 54. The pads 56 and 57 are in longitudinal alignment and each have a respective face for wiping contact with the wall 15 of the borehole 2 to thereby provide lateral support for the end portions 53 and 54 respectively of the second drill stem 50.

The intermediate portion 55 of the second drill stem 50 is substantially similar to the intermediate portion 20 of the first drill stem 4 and has a plurality of longitudinally spaced and aligned pads 58 thereon with the pads 58 on the intermediate portion 55 being positioned in diametrically opposed relation with the pads 56 and 57 on the end portions 53 and 54 of the second drill stem 50. The pads 58 on the intermediate portion 55 of the second drill stem 50 are positioned in longitudinally aligned relation with the pads 21 on the intermediate portion 20 of the first drill stem 4 whereby the first drill stem 4 and the second drill stem 50 are positioned in longitudinally aligned relation and with the longitudinal axis thereof aligned.

The pads 21 on the intermediate portion 20 of the first drill stem 4 and the pads 58 on the intermediate portion 55 of the second drill stem 50 are in wiping contact with the wall 15 and cooperate to provide lateral support for the drill stem 4 and the second stem 50 and maintain the drill bit 8 on a desired drilling axis.

[t is to be understood that while I have illustrated and described one form of my invention, it is not to be limited to the specific form or arrangement of parts herein described and shown.

What I claim and desire to secure by Letters Patent l. A drill collar comprising:

a. an elongated tubular drill stern having a longitudinal axis and opposite ends adapted for connection into a drilling string between a drill bit and a column of drill pipe to provide the stem for the drill bit, said drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said drill stem having a cross section smaller than said upper end portion and said lower end portion, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem;

b. at least one pad secured to said upper end portion and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion having a face for wiping contact with a wall of a borehole to provide lateral support for said drill stern; and

c. at least one pad secured to said intermediate portion of said drill stem and extending around a minor portion of a peripheral surface of said intermediate portion and positioned in diametrically opposed relation with said pad on said upper end portion.

2. A drill collar as set forth in claim 1 wherein:

a. said intermediate portion of said drill stem has a plurality of longitudinally spaced and aligned pads secured thereon; and

b. each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.

3. A drill collar as set forth in claim 1 wherein:

a. said lower end portion has at least one pad secured thereto and extending around a minor portion of a peripheral surface thereof;

b. the pad on said lower end portion is in longitudinal alignment with said pad on said upper end portion; and

c. said pad on said lower end portion has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on upper end portion whereby the face of said pad on said lower end portion is spaced from the wall of the borehole both when the drill bit is spaced from the bottom of the borehole and when the weight of the drilling string is on the drill bit and said drill stem is being rotated.

4. A drill collar as set forth in claim 1 wherein:

a. said intermediate portion of said drill stem has a plurality of longitudinally spaced and aligned pads secured thereon;

b. said drill stem includes a first tapered portion extending between said upper end portion and said intermediate portion of said drill stem;

c. said drill stern includes a second tapered portion extending between said lower end portion and said intermediate portion of said drill stem;

d. a major portion of the peripheral surface of said intermediate portion of said drill stem is arcuate;

e. a minor portion of the peripheral surface of said intermediate portion of said drill stem is flat; and

f. said plurality of pads on said intermediate portion of said drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface.

5. A drill collar as set forth in claim 1 wherein:

a. a major portion of the peripheral surface of said intermediate portion of said drill stem is arcuate b. a minor portion of the peripheral surface of said intermediate portion of said drill stem is flat;

c. said intermediate portion of said drill stem has a plurality of longitudinally spaced and aligned pads secured thereon; and

(1. said plurality of pads on said intermediate portion of said drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically, opposed relation with said flat surface.

6. A drilling string as set forth in claim 5 wherein each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.

7. A drilling string comprising:

a. a column of drill pipe;

b. a drill bit having a plurality of cutting cones, one

of said cutting cones being adapted to cuttingly engage a wall and a bottom of a borehole to thereby define the gauge of the borehole, the other of said cutting cones being adapted to engage the bottom of the borehole;

c. an elongated tubular drill stem having a longitudinal axis and opposite end adapted for connection into said column of drill pipe and to said drill bit, said drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said drill stem having a cross section smaller than said upper end portion and said lower end portion, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem;

d. at least one pad secured to said upper end portion and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion having a face for wiping contact with a wall of a borehole to provide lateral support for said drill stem; and

e. a plurality of longitudinally spaced and aligned pads secured to said intermediate portion of said drill stem with each of said plurality of pads extending around a minor portion of a peripheral surface of said intermediate portion, said plurality of pads being positioned in diametrically opposed relation with said pad on said upper end portion.

8. A drilling string as set forth in claim 7 including means on said lower end portion of said drill stem for effecting longitudinal alignment of said one cutting cone and said pad on said upper end portion of said drill stem.

9. A drilling string as set forth in claim 7 wherein each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.

10. A drilling string as set forth in claim 7 including:

a. a second drill stem having a longitudinal axis and opposite ends adapted for connection into said column of drill pipe and to said first named drill stem, said second drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said second drill stem having a cross section smaller than said upper end portion and said lower end portion of said second drill stem, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem;

b. at least one pad secured to said upper end portion of said second drill stem and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion of said second drill stem having a face for wiping contact with a wall of borehole to provide lateral support for said second drill stem;

c. at least one pad secured to said lower end portion of said second drill stem and extending around a minor portion of a peripheral surface thereof, said pad on said lower end portion of said second drill stem being in longitudinal alignment with said pad on said upper end portion of said second drill stem and in longitudinally aligned relation with said pads on said upper end portion of said first named drill stem and in longitudinally opposed relation with said plurality of pads on said intermediate portion of said first named drill stem; and

d. a plurality of longitudinally spaced and aligned pads secured to said intermediate portion of said second drill stem each extending around a minor portion of a peripheral surface of said intermediate portion of said second drill stem, said plurality of pads on said intermediate portion of said second drill stem being positioned in diametrically opposed relation with said pad on said upper end portion and said pad on said lower end portion of said second drill stem and in diametrically opposed relation with said pad on said upper end portion of said first named drill stem.

11. A drilling string as set forth in claim 10 wherein:

a. a major portion of the peripheral surface of said intermediate portion of said second drill stem is arcuate;

b. a minor portion of the peripheral surface of said intermediate portion of said second drill stem is flat; and

c. said plurality of pads on said intermediate portion of said second drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface.

12. A drilling string as set forth in claim 10 wherein:

a. said second drill stern includes a first tapered portion extending between said upper end portion and said intermediate portion of said second drill stern;

b. said second drill stem includes a second tapered portion extending between said lower end portion and said intermediate portion of said second drill stem;

c. a major portion of the peripheral surface of said intermediate portion of said second drill stem is arcuate;

d. a minor portion of the peripheral surface of said intermediate portion of said second drill stem is flat; and

e. said plurality of pads on said intermediate portion of said second drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface of said intermediate portion of said second drill stem. 

1. A drill collar comprising: a. an elongated tubular drill stem having a longitudinal axis and opposite ends adapted for connection into a drilling string between a drill bit and a column of drill pipe to provide the stem for the drill bit, said drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said drill stem having a cross section smaller than said upper end portion and said lower end portion, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem; b. at least one pad secured to said upper end portion and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion having a face for wiping contact with a wall of a borehole to provide lateral support for said drill stem; and c. at least one pad secured to said intermediate portion of said drill stem and extending around a minor portion of a peripheral surface of said intermediate portion and positioned in diametrically opposed relation with said pad on said upper end portion.
 2. A drill collar as set forth in claim 1 wherein: a. said intermediate portion of said drill stem has a Plurality of longitudinally spaced and aligned pads secured thereon; and b. each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.
 3. A drill collar as set forth in claim 1 wherein: a. said lower end portion has at least one pad secured thereto and extending around a minor portion of a peripheral surface thereof; b. the pad on said lower end portion is in longitudinal alignment with said pad on said upper end portion; and c. said pad on said lower end portion has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on upper end portion whereby the face of said pad on said lower end portion is spaced from the wall of the borehole both when the drill bit is spaced from the bottom of the borehole and when the weight of the drilling string is on the drill bit and said drill stem is being rotated.
 4. A drill collar as set forth in claim 1 wherein: a. said intermediate portion of said drill stem has a plurality of longitudinally spaced and aligned pads secured thereon; b. said drill stem includes a first tapered portion extending between said upper end portion and said intermediate portion of said drill stem; c. said drill stem includes a second tapered portion extending between said lower end portion and said intermediate portion of said drill stem; d. a major portion of the peripheral surface of said intermediate portion of said drill stem is arcuate; e. a minor portion of the peripheral surface of said intermediate portion of said drill stem is flat; and f. said plurality of pads on said intermediate portion of said drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface.
 5. A drill collar as set forth in claim 1 wherein: a. a major portion of the peripheral surface of said intermediate portion of said drill stem is arcuate b. a minor portion of the peripheral surface of said intermediate portion of said drill stem is flat; c. said intermediate portion of said drill stem has a plurality of longitudinally spaced and aligned pads secured thereon; and d. said plurality of pads on said intermediate portion of said drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface.
 6. A drilling string as set forth in claim 5 wherein each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.
 7. A drilling string comprising: a. a column of drill pipe; b. a drill bit having a plurality of cutting cones, one of said cutting cones being adapted to cuttingly engage a wall and a bottom of a borehole to thereby define the gauge of the borehole, the other of said cutting cones being adapted to engage the bottom of thE borehole; c. an elongated tubular drill stem having a longitudinal axis and opposite end adapted for connection into said column of drill pipe and to said drill bit, said drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said drill stem having a cross section smaller than said upper end portion and said lower end portion, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem; d. at least one pad secured to said upper end portion and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion having a face for wiping contact with a wall of a borehole to provide lateral support for said drill stem; and e. a plurality of longitudinally spaced and aligned pads secured to said intermediate portion of said drill stem with each of said plurality of pads extending around a minor portion of a peripheral surface of said intermediate portion, said plurality of pads being positioned in diametrically opposed relation with said pad on said upper end portion.
 8. A drilling string as set forth in claim 7 including means on said lower end portion of said drill stem for effecting longitudinal alignment of said one cutting cone and said pad on said upper end portion of said drill stem.
 9. A drilling string as set forth in claim 7 wherein each of said plurality of pads on said intermediate portion of said drill stem has a face spaced from the longitudinal axis of said drill stem a distance less than the spacing between the longitudinal axis of the drill stem and the face of said pad on said upper end portion whereby the face of each of said pads on said intermediate portion of said drill stem is spaced from the wall of the borehole when the drill bit is spaced from a bottom of the borehole and in wiping contact with the wall of the borehole when the weight of the drilling string is on the drill bit and said drill stem is being rotated.
 10. A drilling string as set forth in claim 7 including: a. a second drill stem having a longitudinal axis and opposite ends adapted for connection into said column of drill pipe and to said first named drill stem, said second drill stem having an upper end portion and a lower end portion and an intermediate portion therebetween, said intermediate portion of said second drill stem having a cross section smaller than said upper end portion and said lower end portion of said second drill stem, said intermediate portion having the center of gravity thereof positioned laterally of the longitudinal axis of said drill stem; b. at least one pad secured to said upper end portion of said second drill stem and extending around a minor portion of a peripheral surface thereof, said pad on said upper end portion of said second drill stem having a face for wiping contact with a wall of borehole to provide lateral support for said second drill stem; c. at least one pad secured to said lower end portion of said second drill stem and extending around a minor portion of a peripheral surface thereof, said pad on said lower end portion of said second drill stem being in longitudinal alignment with said pad on said upper end portion of said second drill stem and in longitudinally aligned relation with said pads on said upper end portion of said first named drill stem and in longitudinally opposed relation with said plurality of pads on said intermediate portion of said first named drill stem; and d. a plurality of longitudinally spaced and aligned pads secured to said intermediate portion of said second drill stem each extending around a minor portion of a peripheral surface of said intermediate portion of said second drill stem, said plurality of pads on said intermediate portion of said second drill stem being positioned in diametrically opposed relation with said pad on said upper end portion and said pad on said lower end portion of said sEcond drill stem and in diametrically opposed relation with said pad on said upper end portion of said first named drill stem.
 11. A drilling string as set forth in claim 10 wherein: a. a major portion of the peripheral surface of said intermediate portion of said second drill stem is arcuate; b. a minor portion of the peripheral surface of said intermediate portion of said second drill stem is flat; and c. said plurality of pads on said intermediate portion of said second drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface.
 12. A drilling string as set forth in claim 10 wherein: a. said second drill stem includes a first tapered portion extending between said upper end portion and said intermediate portion of said second drill stem; b. said second drill stem includes a second tapered portion extending between said lower end portion and said intermediate portion of said second drill stem; c. a major portion of the peripheral surface of said intermediate portion of said second drill stem is arcuate; d. a minor portion of the peripheral surface of said intermediate portion of said second drill stem is flat; and e. said plurality of pads on said intermediate portion of said second drill stem are mounted on said arcuate surface with each of said plurality of pads being positioned in diametrically opposed relation with said flat surface of said intermediate portion of said second drill stem. 